Midi Canal, also called Languedoc Canal, French Canal du Midi or Canal du Languedoc, historic canal in the Languedoc region of France, a major link in the inland waterway system from the Bay of Biscay of the Atlantic Ocean to the Mediterranean Sea. It was built in the 17th century at a time when France was the centre of civil engineering excellence. The Midi Canal connects Toulouse, using water from an artificial reservoir built in the Montagne Noire (Black Mountain), with the Mediterranean at Sète via the Étang de Thau (Thau Lagoon). On its 240-km (149-mile) journey, the Midi Canal first rises 63 metres (206 feet), via 26 locks, on its 51.5-km (32-mile) stretch from Toulouse to its 5-km- (3-mile-) long summit, then descends 189 metres (620 feet) in 183.5 km (114 miles) by 74 locks to Étang de Thau. Following World War II, the canal became important for leisure boating, for which reason it is now the most heavily used canal in France. The Midi Canal was Europe’s first long-distance canal and was designated a UNESCO World Heritage site in 1996.

After Leonardo da Vinci designed the first mitre gates in Milan (1497), he was brought to France in 1516 by Francis I, king of France and Milan. Leonardo looked at proposals for canals from the Garonne River to the Aude River and from the Loire River to the Saône River. The second was considered too difficult, but as the Hers and Fresquel, tributaries of the Garonne and Aude rivers, have sources just a few miles apart, a canal between them was considered possible, though the lack of a local water supply for the summit frustrated engineers for the next century and a half.

The idea of a canal to link the Atlantic and Mediterranean was not abandoned, however. Pierre-Paul, Baron Riquet de Bonrepos, together with his engineer, François Andreossy, finally overcame the main design problem of providing a sufficient water supply system for the summit with plans for building a dam. Louis XIV granted permission for the construction of the canal in 1666, Riquet’s case having been supported by the finance minister, Jean-Baptiste Colbert. Work was soon under way on the water supply system, the most difficult part being construction of the Saint-Ferréol Dam. It is 780 metres (2,560 feet) in length and 32 metres (105 feet) in height, and it holds 6,374,000 cubic metres (about 1,402,100,000 gallons) of water. At the time, it was the greatest civil engineering work in Europe, holding back waters from the Montagne Noire, including the Laudot River, which could feed either the canal or the reservoir via two channels with a total length of 66 km (41 miles).

Seventeenth-century map showing the route and tributary waters of the “New Languedoc …

Despite political and financial pressure, Riquet pushed ahead with construction of the canal, though it affected his health. He died eight months before his canal opened in May 1681. In addition to some 100 locks, the project required building numerous bridges, an aqueduct, and the world’s first canal tunnel. The Malpas Tunnel was 165 metres (541 feet) long and 7.4 metres (24 feet) wide, and it was 5.85 metres (19 feet) above water level; for some reason, it was built to much more generous proportions than any of the canal’s bridges. There were many problems during construction. One lock collapsed in 1670, and Riquet had to redesign and rebuild those already constructed. The canal also had to pass a steep rocky slope at Pechlaurier, and there gunpowder was used—perhaps the first use of explosives for civil engineering. At one time 12,000 people were working under Riquet’s command, the labour force being split into 12 divisions so that control could be maintained.

Following Riquet’s death, his sons, together with the celebrated French engineer Sébastien Le Prestre de Vauban, continued work on improving the canal. By 1692 these improvements had been completed, and travelers from around the world came to examine the canal. Although it was fairly successful financially, the canal never carried ships from the Atlantic to the Mediterranean. Until the Canal de Beaucaire opened from Sète to the Rhône in 1808, the Midi Canal was isolated from the rest of France’s canal system. Between 1850 and 1856, the western end of the canal was extended by 193 km (120 miles) with the building of the Canal Latéral à la Garonne. The locks on both canals were shorter, at 30 metres (98 feet), than the standard French dimensions of 38.5 metres (126 feet) introduced in 1879 by Charles de Freycinet, the minister of public works, and the maximum weight a barge could carry on the canals was 160 tons. Because of this, the Midi Canal never carried a significant volume of goods to destinations outside of its immediate region.

The locks on the Canal Latéral were lengthened in the 1970s to the Freycinet standard length, though those on the Midi Canal remained at their original size. As part of a plan to allow standard French barges to use the canals, two unique “water slopes” were built at Montech on the Canal Latéral à la Garonne in 1974 and at Fonserannes on the Midi Canal in 1983. On these water slopes, boats are raised and lowered along an inclined channel in a wedge of water created by a moveable barrier within the channel. Despite these improvements, commercial traffic declined rapidly on the canals, though some barges still operate on the Canal Latéral.